Page 308 - Deep Learning

9

The Formation of Belief

Any statement can be held true come what may, if we make drastic enough adju st­
ments elsewhere in the system [of beliefs].
W. v. Quine 1

To someone standing on the African savannah, walking across a field in the
Fertile Crescent or riding across the north American prairie, the evidence of
the senses is unequivocal: The earth is flat. There are local perturbations –
valleys and mountains – but they cancel each other over long distances, so
the earth extends in all directions in the horizontal plane. Although it is dif-
ficult to prove anything about the beliefs of pre-historic peoples, it would be
surprising if they conceived of the earth in any other way. But the flat earth
generates puzzles: How far does it extend? Does it have an edge? if so, what is
beyond the edge? if the ocean extends all the way to the edge, what happens
with the water? if it pours over the edge, must not the ocean empty out eventu-
ally? Where does the water go? To anyone with the disposition and the oppor-
tunity to consider such questions, the lack of intelligible answers must have
generated doubt. People living by the sea could make two observations that
point to a different conception: Looking out from a high observation point, an
observer sees the horizon curve ever so slightly. When a ship approaches, the
mast appears over the horizon before the hull.
By the fourth century b.c., Greek philosophers, Aristotle prominent among
them, had drawn the right conclusion from these and related observations,
and in the third century b.c. the Alexandrian scholar eratosthenes engaged
in an astonishingly successful attempt to estimate the size of what he believed
to be a spherical earth. However, such intellectual exercises were confined
2
to a small portion of the earth’s population, and belief in the spherical shape
of the earth did not become common in europe until after the Middle Ages.
eventually, astronomy and ocean navigation settled the issue for the elites,

291